Optical communication systems are known in which optical signals carrying data are transmitted from a first node (e.g., a transmitter (Tx)) to a second node (e.g., a receiver (Rx)) via an optical fiber. At the Rx, the optical signal is converted into corresponding electrical signals, which are then further processed.
In some cases, the Rx may include a coherent Rx. In a coherent Rx, a received signal is mixed with an output of a local oscillator (LO) in an optical hybrid circuit, the outputs of which are provided to photodetectors to generate analog electrical output signals. For example, the analog signals may be sampled at a sample rate by analog-to-digital converter (ADC) circuits configured to supply outputs for further processing by a digital signal processor (DSP) included in the coherent Rx. Thus, for the coherent Rx, the amplitude, phase, and state of polarization of the optical signal are all transferred to the electrical domain for digital signal processing in the Rx DSP.
While travelling through the fiber (e.g., from the Tx to the Rx), the optical signal may experience impairments and/or changes, such as chromatic dispersion (CD), polarization mode dispersion (PMD), and/or a change in a state of polarization. As a result of such impairments and/or changes, electronic signals, representative of data carried by the optical signal, may have different delay, frequency response, and polarization characteristics.